In the improvement of weapon systems, emphasis is placed on increased efficiency in using propellant energy and thus achieving higher projectile velocities. Reduced time of flight of the projectile, improved accuracy, and improved terminal ballistics can be obtained through higher velocity. A practical advanced weapon system concept dictates that consideration be given to weapon and ammunition cost, size, weight, and improved performance.
Today's state-of-the-art weapons have evolved from using a straight cased configuration, utilizing fast-burning black powder, to a bottleneck case, employing slower burning, higher pressure, smokeless propellants. Configurations which have been at least partially successful in the development stages are: folded rounds, which further utilize the bottleneck principle in providing a combustion chamber aside from the bore centerline; telescoped rounds; liquid propellant configurations; consolidated propellants; and various configurations utilizing programmed propellant. Characteristically, all of these gun systems have exhibited disproportional peak chamber pressure increases to muzzle velocity increases. The mass relationship of launched mass and propellant tends to get out of hand, amplifying the peak pressure problems, when velocities exceeding 5000 feet per second (fps) are desired. The increased quantity of propellant required to impart higher energies to the projectile produces a larger mass of gas, which must also be accelerated. Since a large part of the propellant is ignited in the chamber, the pressure rise is rapid, and the major part of the velocity is developed early in the innerballistic function. The projectile displacement establishes high volume increase rates relative to propellant gas expansion, resulting in a rapid pressure decay. In the lower pressure environment, burn rate of remaining propellant is not adequate to sustain the higher pressure levels. The parasitic energies involved in accelerating the gas mass proportional to projectile displacement result in significantly reduced efficiency and ultimately establish a practical velocity limit. None of the previously mentioned rounds and weapon systems have satisfactorily solved the size and pressure problems associated with a practical, produceable, repeating type gun system for velocities in excess of 6000 fps.